Method of conditioning tobacco



Feb. 25, 1969 KOCH ET AL METHOD OF CONDITIONING TOBACCO Sheet Qrigmal Filed Nov. 17, 1964 aw mm 3 @mm 5 Q 1 92mm MQQRQDZ k mw Inventors HA NS KOCH WALDEMAR WOCHNOWSK/ THE/R ATTORNEY Feb. 25, 1969 KOCH ET AL 3,429,317

METHOD OF CONDITIONING TOBACCO Origlnal Filed Nov. 17. 1964 Sheet 2 0f 6 MEASURING BRIDGE FOR TEMPERATURE Fig.4

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WALDEMAR WOCHNO WS K BY 'ifi THE/R ATTORNEY Feb. 25, 1969 KOCH ET AL 3,429,317

METHOD OF CONDITIONING TOBACCO Original Filed Nov. 17, 1964 Sheet 5 0f 6 N v\ 2 C N N 1% Tl go Inventors: HANS KOCH WALDEMAR WOCHNOWSK/ By 1 r g L k *w m :LL":

THE/R A TTORNEY Feb. 25, 1969 KQCH ET AL 3,429,317

METHOD OF CONDITIONING TOBACCO Original Filed Nov. 17, 1964 Sheet of a 00 TPU 7' Inventors: HANS KOCH WALDEMAR WOCHNOWSK/ THE/RATTORNEY United States Patent Q 3,429,317 METHQD F CONDITEONING TOBACCO Hans Koch, Meiendorferweg 22, Hamburg-Rahlstedt, Germany, and Waldemar Wochnowski, Eulenkrugstrasse 143, Hamburg-Voiksdorf, Germany Original application Nov. 17, 1964, Ser. No. 411,788, new Patent No. 3,372,488, dated Mar. 12, 1968. Divided and this application Jan. 4, 1968, Ser. No. 695,672 Claims priority, application Great Britain, Nov. 18, 1963,

45,434/ 63 U.S. Cl. 131-440 Int. Cl. A24b 9/00; F26b 3/04 10 Claims ABSTRACT OF THE DISCLOSURE Crass reference to related application This is a division of our copending application Ser. No. 411,788, filed Nov. 17, 1964, now Patent No. 3,372,- 488, granted Mar. 12, 1968.

Background of the invention The present invention relates to a method of conditioning tobacco, and more particularly to improvements in a method of drying whole or shredded tobacco leaves. Still more particularly, the invention relates to a method of drying tobacco by means of two fluids, such as hot air and steam.

In conditioning of tobacco, it is important that the moisture content of tobacco should remain constant. Tobacco which is too moist might contaminate certain parts of the machine to bring about disturbances and lengthy interruptions in operation. Also, and when the tobacco is used in the manufacture of cigarettes, excessive or insufficient moisture content might affect the quality of cigarettes. A particularly serious drawback of tobacco Whose moisture content varies is that changes in moisture content affect the weight of cigarettes. If the tobacco is too dry, the weight of cigarettes is reduced and, in order to increase the weight, the manufacturer must use more tobacco which adds considerably to the manufacturing cost. Dry tobacco breaks up easily and produces too much dust.

Summary of the invention It is an object of our invention to provide a novel method of conditioning tobacco in such a way that the moisture content of conditioned tobacco corresponds exactly to or approximates very closely the desired moisture content, that the moisture content can be maintained at a desired value despite eventual changes in the rate (in kilograms per hour) at which tobacco is being fed to the conditioning apparatus, and that the conditioning operation can be carried out by full consideration of all such factors which might affect the moisture content of treated material.

Another object of the invention is to provide a method according to which large quantities of tobacco can be conditioned per unit of time and which can be employed with equal advantage for treatment of tobacco leaves or ice for treatment of shredded or otherwise comminuted tobacco.

Briefly stated, one feature of our invention resides in the provision of a method of controlling the moisture content of tobacco which contains a surplus of moisture. The method comprises conveying a stream of moist tobacco through a conditioning zone in which the tobacco is relieved of surplus moisture by exchanging heat with two fluids one of which expels from tobacco some surplus moisture and the other of which expels from tobacco the remainder of surplus moisture, measuring the moisture content of the stream ahead of the conditioning zone, adjusting the exchange of heat between the tobacco stream and the one fluid when the measured moisture content deviates from a predetermined value, measuring the weight of tobacco per unit length of the tobacco stream ahead of the conditioning zone, and adjusting the exchange of heat between the stream and the one fluid when the measured Weight deviates from a predetermined value.

In accordance with another feature of the present invention, the method may include the additional steps of measuring the moisture content of conditioned tobacco at a point downstream of the conditioning zone and adjusting the exchange of heat between the tobacco stream and the other fluid when the measured moisture content of conditioned tobacco deviates from a predetermined value. The adjustments in exchange of heat between the tobacco stream and the other fluid may be eiiected in stepwise fashion and the arrangement is preferably such that the one fluid (for example, heated air) exchanges heat with the tobacco stream before the tobacco is treated by the other fluid. If necessary, the ratio of surplus moisture which is expelled by the fluids may be varied, i.e., one of the fluids may expel a greater or lesser percentage of surplus moisture and the other fluid then expels the remainder of such surplus moisture. The one fluid is preferably brought into direct heat exchanging contact with the tobacco stream and the exchange of heat between the tobacco stream and the other fluid preferably takes place indirectly, for example, through the walls of a drier which defines the conditioning zone.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved method itself, however, will be best understood upon perusal of the following detailed description of an apparatus which can be used in carrying out the method and which is illustrated in the accompanying drawing.

Brief description of the drawing FIG. 1 is a diagrammatic side elevational view of an apparatus for conditioning shredded tobacco in accordance with the method of our invention;

FIG. 2 is an enlarged transverse vertical sectional view as seen in the direction of arrows from the line 11-11 of FIG. 1 and illustrates a portion of a dielectric moisture detector;

FIG. 3 is a diagram showing the manner in which the temperature of heated air changes in response to changes in the rate of tobacco flow and/or in response to changes in the moisture content of incoming tobacco;

FIG. 4 is a diagrammatic view of a circuit showing the elements of and the connections between the devices which sense and measure the temperature and the moisture content of tobacco in the apparatus of FIG. 1;

FIG. 5 is a schematic view of a servo amplifier unit employed in the apparatus of FIG. 1;

FIG. 6 is a diagrammatic view of a temperature measuring device in the apparatus of FIG. 1;

FIG. 7 is a diagrammatic view of a control amplifier in the apparatus of FIG. 1;

FIG. 8 is a diagrammatic view of a time-delay device which is employed in the apparatus of FIG. 1;

FIG. 9 is a diagrammatic view of a modified timedelay device; and

FIG. 10 is a diagrammatic view of a pressure gauge and of means for sensing changes therein.

Description of the preferred embodiments Referring to FIG. 1, there is shown a conditioning apparatus for tobacco including an inclined cylindrical drier I mounted on rollers 4 provided at the upper ends of supporting legs 2 and 3. The drier comprises an annulus of teeth 6 which mesh with a pinion 5. The latter is driven by an electric motor a through the intermediary of a variable speed transmission 5b. The apparatus further comprises an electric heater 7 which is provided at one end of the dried 1 and serves to heat a current of air which enters in the direction indicated by arrows 7a. Such air is drawn by a suction fan 8 whose suction side is con nected with a suction duct 8a, and the inlet of the suction duct 8a accommodates the heater 7. The pressure side of the fan 8 is connected with a supply duct 29 which directs the current of preheated air into the left-hand end (intake end) of the conditioning chamber or zone 1a defined by the drier 1. The suction duct 8a has a lateral inlet opening which may be sealed or exposed by a damper valve 9 to admit requisite quantities of unheated air into the current of preheated air which flows to the fan 8, i.e., the temperature of the air current in the supply duct 29 may be regulated independently of the heater 7 by changing the position of the valve 9. The direction in which a second current of air may be admitted into the suction duct 8:: is indicated by an arrow 7b. The heater 7 may but need not be of the adjustable type and this heater may be replaced by an oil, gas or steam heater.

The conditioning chamber 1a of the drier 1 accommodates a series of heating coils 10 which convey steam or another heating fluid. The inlets of the coils 10 are connected to a header 11a which receives steam from a supply conduit 11 provided with a suitable steam valve 12. The supply conduit 11 is located at the right-hand end (discharge end) of the drier 1. This discharge end is closed by a hood 18 which serves to collect spent air and accommodates a filtering drum 20 driven by an electric motor 19. The hood 18 is connected with an evacuating conduit 21 provided with an adjustable valve 23 and connected to the suction side of an exhaust fan 22. Instead of conveying steam, the supply conduit 11 may admit hot combustion products or another fluid medium.

The material to be conditioned forms a stream T of shredded tobacco particles which are fed by an endless belt conveyor 13 to descend onto the upper stringer of a second belt conveyor 13a cooperating with a weighing device 54. From the belt conveyor 13a, the stream T descends into a channel 16 forming part of a dielectric moisture detector 25 and thereupon into an inclined chute 17 which feeds the particles into the intake end of the drier 1. The channel 16 is vibrated by an electric motor 14 through the intermediary of an eccentric 15.

The channel 16 is shown in FIG. 2. It comprises a centrally located V-shaped measuring trough 24 which is completely filled with tobacco. The remainder of tobacco descends into lateral troughs 24a. The manner in which the dielectric detector 25 determines the moisture content of tobacco in the trough 24 is disclosed in Patent No. 3,320,528 to Esenwein. This detector 25 determines the percentage of moisture in the tobacco stream and feeds such information to a control amplifier 26 which sends electrical impulses through a time delay device 27 to a synchronizing device 28.

A temperature measuring device 30 extends into the supply duct 29 and is connected with the synchronizing device 28 through a control amplifier 31. The measuring device 30 enables the apparatus to regulate the temperature of the air current which enters at 7a by controlling the position of the valve 9. This valve is connected with the synchronizing device 28 through a control amplifier 34, a servo amplifier unit 33 which converts electrical impulses into mechanical impulses, and a servomotor 32 which is coupled to the valve 9. In the area of the valve 9, there are provided two limit switches 35, 36 which are connected to a control amplifier 37 and to a programming device 38. The programming device 38 is connected with the synchronizing device 28. The temperature measuring device 30, the control amplifiers 31, 34, the servo amplifier unit 33 and the servomotor 32 constitute a temperature regulating circuit which also includes a rated value selecting or setting device 39 connected with the synchronizing device 28.

An endless belt conveyor 40 is located at a level beneath the discharge end of the drier 1 and receives the stream T' of conditioned tobacco to deliver the stream to the channel 41 of a second dielectric moisture detector 42 which is identical with or analogous to the aforementioned detector 25. This second dielectric detector 42 is connected with a control amplifier 43 and with a synchronizing device 52. The device 52 is connected with a second rated value selecting or setting device 44. The valve 12 is adjustable by a servomotor 48 which receives impulses from a servo amplifier unit 47 connected with the synchronizing device 52 and with two control amplifiers 45, 46. The devices 42, 43, 44, 45, 46, 47 and 48 form a moisture regulating circuit which will detect and, if necessary, control the moisture content of tobacco in the stream T issuing from the drier 1. The tobacco stream T passing through and beyond the channel 41 is fed onto the upper stringer of a takeoff belt 57 which delivers the stream to the next processing station, for example, to a cigarette machine. The temperature regulating circuit 3044, 39 is completed by the tobacco passing through the channel 16 and by heated air passing through the supply duct 29.

A third regulating circuit comprises a pressure gauge 49 which measures the stream pressure in the conduit 11 downstream of the valve 12 and a control amplifier 50 which is connected in the conductor between the control amplifiers 45, 46. This third circuit is integrated into the second circuit and includes the parts 12, 46, 47, 48, 49 and 50. The amplifier 47 produces an electric current which charges a time delay device 51 and produces a discharge current in a conductor 53 connecting the device 51 with the synchronizing device 52.

In accordance with a feature of the present invent-ion, the belt conveyor 13a cooperates with the weighing device 54 which is connected with the synchronizing device 28 through a control amplifier 55 and a time delay device 56. The weighing device 54 determines the quantity of tobacco per unit of time (for example, in kilograms per hour) and feeds such information to the amplifier 55 which produces electrical impulses and sends such impulses to the synchronizing device 28. The first regulating circuit 30-34, 39 is controlled by the impulses which are transmitted by the amplifiers 26, 55 through the time delay devices 27, 56 and which are respectively generated by the measuring device 25 and weighing device 54. The limit switches 35, 36 eifect stepwise return movement of the valve 9 into a neutral (median) position by simultaneous stepwise regulation of the heating effect upon the walls of the drier 1.

Referring to FIG. 4, there is shown the electric circuit of the devices 25 to 27. It will be seen that the tobacco stream T whose moisture content is to be measured passes through the channel 16 one end portion of which supports a measuring condenser 25a. Frequency and oscillation amplitude of the channel 16 (and hence the speed of the tobacco stream T and the limits of the measuring trough 24) are controlled in such a way that the trough 24 always contains the same quantity of tobacco particles.

The condenser 25a forms part of a high frequency oscillating circuit which further includes three condensers C25, C26, C27, a coil L4, and a variable rotary condenser CW which is driven at constant speed by a motor M. Coils L2, L3 and a condenser CK couple the high frequency oscillating circuit in three-point connection with a high frequency generator formed of a pentode VI, a coil L1 and condensers C16, C19. R30 is a grid leak resistors, and R31 is a grid resistor. Condensers C18, C17 couple the high frequency generator with a high frequency rectifier V5/1. The control grid grid of pentode V3 is actuated through a resistor R32. The plate voltage of the pentode V3 actuates the screen grid of the pentode VI. Condensers C15, C and C21 are filter condensers. R33, R20, R36 and R37 are voltage divider resistors. R34 and R are plate resistors.

A high frequency rectifier V5, resistors R49, R50, a condenser C29 and a pentode V6 form a vacuum tube voltmeter. In the plate circuit of the pentode V6 is inserted a meter 60 to indicate the percentage of moisture. Actuating impulses for the regulation of drying by hot air are taken off at the cathode of the pentode V6 over resistors R52, R54 and a variable resistor (potentiometer) P7. The resistor P7 controls the accuracy of the moisture content measurement. C32 is a filter condenser. R10'1, P2, R55 and R53 are voltage divider resistors. A thermistor TH and resistors R66, R65, R71, R72 and P6 (potentiometer) form a Wheatstone bridge circuit. Voltage changes on the resistor P6 are conducted by potentiometers P3, P2, P7 and resistors R55 and R52 to the suppressor grid of the pentode V6 of the vacuum tube voltmeter. C31 is a filter condenser and R51 is the biasing resistor for the suppressor grid of the pentode V6.

The circuit of FIG. 4 operates as follows:

The motor M drives the rotatable condenser OW at constant speed so that the fundamental frequency of the high frequency circuit L4, C26 and measuring condenser 250 will be periodically varied. The frequency of the high frequency generator is amplitude stabilized by means of coupling of tubes V5 and V3, and this frequency is so selected that it lies about in the middle of the periodically changing fundamental frequency. Consequently, the eX- tent of the frequency variation caused by rotation of the condenser CW is selected in such a way that, even when the measuring condenser 25a in the trough 24 is loaded and the predetermined extent of moisture content in the cycle reached, the high frequency circuit will once during each revolution of the rotating condenser CW be in resonance with the high frequency genera-tor within the desired range of the moisture content. In this manner, there will exist at the measuring condenser 25a a high frequency field with the frequency of the high frequency generator the amplitude of which is modulated with the frequency of the rotating condenser CW. Inasmuch as the vacuum tube voltmeter measures only the voltage peaks, and such peaks always bear a linear relationship to the contents (moisture content and quantity) of the measuring condenser 25a, the indicator of the vacuum tube voltmeter can be calibrated to indicate the percentage of moisture content.

Inasmuch as, with every high frequency measurement, here also the measurement indication depends on the temperature of the contents of the measuring condenser 25a, this condenser has built into it the temperature feeler or sensor TH so that one receives at the potentiometer P6 of the Wheatstone bridge circuit voltage changes which correspond to changes in tobacco temperature. Such voltage changes will vary the grid potential of the pentode V6 of the vacuum tube voltmeter so that faulty measurements because of temperature variations of the tobacco stream T are compensated for. The voltages appearing at the cathode of the pentode V6 are hence a measure of the moisture content.

The circuit of the devices 42, 43 is analogous to the circuit of FIG. 4.

Referring to FIG. 5, there is shown the circuit of the servo amplifier unit 33 which is employed in the apparatus of FIG. 1 for the purpose of adjusting the servomotor 32 in response to impulses received from the control amplifier 34.

There are two output relays A and B one of which will operate to make a positive correction, that is to say to remedy a positive deviation. The other relay will .be operated to correct what could amount to a negative deviation from normal operation. The resistors R6 and R6, in connection with the Zener diodes ZMl and ZM2 stabilize the operating voltage of the push-pull first stage of the amplifier which includes transistors T and T working resistors R and a common emitter resistor R The first stage of the amplifier is followed by a Schmitt trigger stage with relay outputs. The Schmitt trigger stages include transistors T T and T T respectively, resistors R7, R5, R8, R9 and R10, R11, R12, R13, respectively, and the output relays A, B respectively. The diodes D1 and D2 are protective diodes. Referring further to the circuit shown in FIG. 5, it will be seen that a signal or impulse received from -the amplifier 34 will appear as a signal across or an entrance resistance RE and this signal will be amplified by the first stage of the amplifier unit 34. Now, depending upon the nature of the signal, that is to say whether it requires a positive correction or a negative correction, the effect will be felt either at a point C near transistor T1, or at a point E near transistor T2. When the signal appearing at C calls for correction, it is fed further into the related Schmitt trigger stage so as to actuate the relay A which may be connected by suitable wiring to close the circuit of the servomotor 32 for correcting in a positive sense the valve 9 in any well known manner. Similarly, if the impulse is registered at point E in FIG. 5, indicating that a negative correction is needed, then that impulse is amplified in the amplifier stage and will influence its corresponding Schmitt trigger stage so as to actuate the relay B and thus bring about a correspondingly desired correction of the position of the valve 9. Relays A and B are as mentioned connectable through power lines to control or regulate the operation of the servomotor 32. The circuit of the amplifier 47 is analogous to the circuit of FIG. 5.

Referring now to FIG. 6, there is shown the circuit of the control amplifier 31 which amplifies the temperature indications of the temperature measuring device 30 and at the same time produces output impulses or voltages responsive to the temperature variations, but in linear relationship to these temperature variations. In order to do this, the circuit shown in FIG. 6 shows the temperature measuring device 30 or as also called a thermistor, feeding into an initial circuit stage with a transistor T1 connected with a resistor R1, Zener diode ZMl and a resistor R2 to maintain at a constant level the current despite the changing resistance of the measuring device 30. The point A is connected through the adapter transistor T2 with the emitter resistor R3 and the resistor R4 to a push-pull amplifier stage T3, T4, R4, R3, R5, R6, R9. This arrangement is followed by a volt age amplifier stage with transistors T5, T6, Zener diode ZM2, and resistors R10, and R7. Referring again to the circuit diagram, P1 is a matching potentiometer and resistors R11, R8 and Zener diode 2M3, ZM4 serve for voltture of the thermistor and the voltage at point A arises. In the push-pull amplifier stage which includes the transistors T3 and T4, for power amplification, the influence of variations in the temperature of surrounding air is eliminated and as a result with voltage amplified by transistors T and T6, there is available at the output terminal of the circuit from transistor T6, a voltage which is in linear correspondence and relationship with the temperature of the measuring device 30.

In FIG. 7 there is shown the circuit diagram of the control amplifier 34 which might be called a regulating amplifier by which amplification is provided for impulses transmitted to the servo amplifier unit 33. As shown in this view, the resistors R7, R8 and the Zener diodes ZM1, and ZM2, serve for the stabilization of the supply voltage. The transistors T1 and T2 with their working resis tors R2 and R3 and the emitter resistor R1 form a pushpull amplifier stage, which is coupled by a coupling network including transistor T3, Zener diode 2M4 and resistor R5 with the transistor T4 and the resistor R6, with a voltage amplifier stage connected to its output, the voltage amplifier stage =being in turn followed by a current amplifier stage which includes the transistor T5 and the two resistors R9 and R10. The operation of the circuit shown in FIG. 7 may be explained briefly as follows. When a signal or impulse coming from the synchronizing device 28 appears at a point A of the input of the control amplifier 34, it will then appear thereafter at point B with its power amplified, and at point C with its voltage amplified, and at point D with its current amplified. Thus it is seen that at the point D of the amplifier a proportionally high amplified deviation signal impulse appears. The push-pull amplifier stage shown in the circuit, renders the control amplifier unresponsive to ambient temperature variations. The circuit of the amplifier 45 or 46 is analogous to the circuit of FIG. 7.

Referring now to FIG. 8, there is shown the circuit of the time delay device 56 which is used in order to delay impulses which are received from the weighing device 54 to be integrated into the circuit at a later stage, namely, at a stage to insure that the temperature of air in the supply duct 29 changes at the time when that portion of the tobacco stream T which has caused the weighing device 54 to send an impulse to the amplifier 55 reaches the intake end of the drier 1. In the circuit the input is shown at the left and the output is shown at the right, it being seen that there is a resistance-capacitance circuit for-med of a variable resistance R1 in series and bridging capacitor C, there being an output series resistor R2 following the capacitor C. In accordance with well known circuit principles, the time constant of the circuit is determined by the values of the resistance R1 and the capacitor, and when the capacitor has been fully charged it then discharges after the predetermined time interval, through output resistor R2 at which time the impulse can be employed in the synchronizing device 28 as explained. The construction of the time delay device 57 is analogous.

FIG. 9 shows the circuit of the time delay device 51. This circuit is of particular utility in connection with the servo amplifier unit 47 shown in FIG. 5. It comprises resistors R1 and R2 connected in series across output terminals plus U, and minus U of the power amplifier circuit .seen in FIG. 5, with their center tap grounded. The movable arms of resistors R1 and R2 are respectively connected to switches K2 and K1 which are normally open and the remote terminals of both switches are connected together and to variable resistor R3 which with capacitor C forms a time delay network somewhat similar to the network .seen in FIG. 8, there being an output series resistor connected to the network, as seen at R4, through which the capacitor C is discharged after the predetermined time interval as set by the time constant of the circuit, thus passing on the impulse after the desired time delay. The impulse is transmitted by closing of either of contacts K1 or K2.

FIG. 10 shows one means for deriving an impulse or signal from the pressure gauge 49. As seen in this brief detailed view, the amplifier includes a potentiometer 50a which may be connected at its ends to a fixed source of voltage and with its movable potentiometer arm connected to an output terminal. The movable potentiometer arm may be rotatable and may be thereby mechanically coupled to the rotatable shaft of the pressure gauge 49 seen in FIG. 1 so that as it assumes one position or another from a zero position or a no position variations in position of its potentiometer arm cause different or varied voltages to appear at the output A. It is also apparent that the circuit of FIG. 10 may also be employed for other purposes relating to various movable parts of the machine seen in FIG. 1 such as to indicate a displacement of a weighing scale on the device 54.

The apparatus of FIG. 1 operates as follows:

The tobacco stream T advances in the direction indicated by an arrow 13b and passes from the belt conveyor 13 onto the belt conveyor 13a so that the weighing device 54 determines the weight per unit of time (kg/h.) and feeds such information to the amplifier 55. The tobacco stream T then advances into the channel 16 of the dielectric detector 25 and the latter determines the moisture content (in percent) of that portion of the tobacco stream which passes through the trough 24 of the channel 16 to deliver corresponding impulses to the amplifier 26. The thus weighed and measured tobacco stream T then enters the chute 17 and is admitted into the drier 1. The drier is inclined downwardly in a direction toward the discharge end so that the stream T advances from the intake end toward the discharge end and is conditioned by hot air issuing from the supply duct 29 and by heat radiated from the cylindrical wall which is heated by the coils 10. The coils 10 carry agitating blades or paddles 10a which exchange heat with tobacco particles to insure more uniform conditioning of the tobacco stream. The current of air issuing from the supply duct 29 is effective mainly in the region of the intake end of the drier 1 because the direction of air flow is concurrent with the direction in which the tobacco stream T advances through the conditioning chamber 1a. The moisture which is withdrawn from the tobacco stream T is evacuated through the hood 18 by passing through the evacuating conduit 23 and to the outlet of the exhaust fan 22.

The tobacco stream T which is discharged from the conditioning chamber 1a of the drier 1 descends onto the belt conveyor 40 and is fed into the channel 41 of the dielectric detector 42 whereby the detector produces impulses which are amplified at 43 and are transmitted to the synchronizing device 52. If the measured result (i.e., the percentage of moisture in the stream T passing in the channel 41) likewise deviates from a desired value, the dielectric detector 42 will initiate a change in the pressure of steam which circulates through the coils 10 to thereby alter the heating efiect upon the tobacco stream in the chamber of the drier 1.

It is now assumed that as the drier 1 rotates, that the heater 7 heats the infiowing air current to a certain temperature, and that the coils 10 heat the cylindrical wall of the drier 10 to a certain temperature so that the tobacco stream T issuing from the chamber In has a moisture content which corresponds exactly to a desired value. In such instance, the sum of all current impulses generated by the devices 25, 54, 30, 29 and transmitted to the synchronizing device 28 equals zero. Thus, the position of the valve 9 remains unchanged. The sum of all impulses transmitted to the synchronizing device 52 also equals zero and the position of the valve 12 remains unchanged.

If the quantity of tobacco in the stream T passing over the belt conveyor 13 changes, the weighing device 54 will cause the amplifier 55 to send an impulse which is delayed by the device 56 and is transmitted to the synchronizing device 28 which sends a corresponding impulse to the servomotor 32 so that the latter adjusts the valve 9 until the ratio of heated air (arrows 7a) to unheated atmospheric air (arrow 7b) is altered sufliciently to insure that the moisture content of tobacco issuing from the drying chamber 1a again equals the desired value. Such adjustment in the temperature of air which comes in contact with tobacco is ettected without delay because the cooling effect of air entering at 9 is instantaneous. Of course, as the temperature of air flowing through the supply duct 29 changes, the measuring device 30 senses such change and causes the amplifier 31 to send an impulse to the synchronizing device 28. The adjustment is terminated when the sum of all impulses transmitted to the device 28 again equals zero. The time delay device 56 is adjusted in such a way that the temperature of the air current flowing into the chamber 1a of the drier 1 is changed at the time the chamber receives tobacco at the new rate. In other words, the delay caused by the device 56 corresponds to the interval necessary for a batch of weighed tobacco to advance from the belt conveyor 13a to the intake end of the drier 1.

The manner in which the drying effect upon the tobacco stream T is changed in response to changes in the rate at which the tobacco particles are admitted into the channel 16 of the dielectric detector can be observed by referring to the diagram of FIG. 3. That portion of the tobacco stream T which is already accommodates in the chamber 1a of the drier 1 is not affected (or is alfected very little) by changes in the temperature of the air current. If the rate of tobacco flow is reduced, the temperature of the air current is also reduced (see the lefthand portion of the lowermost curve in FIG. 3). If the rate at which the tobacco is admitted increases, the temperature of the air current is raised accordingly (see the left-hand portions of the two upper curves in FIG. 3). The straight portions of the curves indicate the temperature in the interior of the chamber 1a.

The just described mode of changing the temperature of the air current is particularly desirable when the rate of tobacco flow is changed for a relatively short period of time and the tobacco thereupon begins to flow at the normal rate. However, if the moisture content of the tobacco stream is aflected by factors other than those which are measured by the weighing device 54, by the temperature measuring device and by the dielectric detector 25, adjustments are made in response to impulses from the dielectric detector 42. Such adjustments will be made in response to longer-lasting disturbances whose duration is such that their efiects are detected by the dielectric detector 42. This detector will sense gradual changes in moisture content and the amplifier 43 sends corresponding impulses to the synchronizing device 52 which causes the servometer 48 to adjust the valve 12 and to thereby change the steam pressure in the coils 10. Thus, the valve 12 will insure that the actual moisture content of tobacco issuing from the drier 1 again equals the desired value.

When the synchronizing device 52 sends impulses to the servomotor 48, such impulses pass through the amplifiers 46, 47 and are communicated to the condenser of the time delay device 51 which is charged and, after a predetermined interval of time, discharges a current through the conductor 53. Such current is proportional to the current flowing tom the generator 43 to the receiving device 52 but of opposite sign. Consequently, the adjustment of the valve 12 through the servomotor 48 is delayed for an interval of time which corresponds to the setting of the time delay device 51. This setting is such that the delay corresponds to the interval of time which elapses from the moment when the steam pressure changes to the moment when the dielectric detector 42 actually detects changes in moisture content in response to such adjustment in steam pressure.

When the steam pressure is adjusted by changing the setting of the valve 12, the pressure gauge will cause the amplifier to send an impulse which will produce a damping effect upon the servomotor 48, i.e., changes in the setting of the valve 12 will be etfected gradually.

If the moisture content of the tobacco stream T changes before the stream actually enters the drier 1, such change is detected by the dielectric detector 25 and the resulting impulse is sent on to the synchronizing device 28 which causes the servomotor 32 to adjust the position of the valve 9 in exactly the same Way as was described in connection with the operation of the weighing device 54. The devices 26, 55 comprise adjusting elements (see FIG. 6) which may change their sensitivity, i.e., which will determine the exact range of changes in the rate of tobacco flow or in the moisture content of incoming tobacco to which the devices 26, 55 respond by producing impulses which effect adjustments in the setting of the valve 9.

The rated value setting device 44 is provided with a potentiometer or a similar selector which enables the operator to select the desired moisture content of tobacco which issues from the drier 1.

If the valve 9 abuts against one of the limit switches 35, 36 for a considerable interval of time, its setting cannot be changed in one direction. This will be readily un derstood since the valve 9 will engage the limit switch 35 or 36 at the time it is moved to one of its extreme positions. In such instance, the corresponding limit switch 35 or 36 initiates an impulse which causes the valve 9 to pivot stepwise and through small increments back toward its neutral position. The duration of adjustment to complete a step equals the time necessary to move a tobacco particle from the intake end to the discharge end of the drier 1. During such stepwise movement of the valve 9 to neutral position, the servomotor 48 effects corresponding adjustments in the setting of the valve 12 to change the heating effect of the coils 10.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A method of controlling the moisture content of tobacco, comprising the steps of conveying a stream of tobacco which contains surplus moisture through a conditioning zone in which the tobacco is relieved of surplus moisture by exchanging heat with two fluids one of which expels from tobacco some surplus moisture and the other of which expels the remainder of surplus moisture; measuring the moisture content of the stream ahead of said conditioning zone; adjusting the exchange of heat between the stream and said one fluid when the measured moisture content deviates from a predetermined value; measuring the weight of tobacco per unit length of the stream ahead of said conditioning zone; and adjusting the exchange of heat between the stream and said one fluid when the measured weight deviates from a predetermined value.

2-. A method as defined in claim 1, further comprising the steps of measuring the moisture content of conditioned tobacco at a point past said conditioning zone, and adjusting the exchange of heat between the stream and said other fluid when the measured moisture content of conditioned tobacco deviates from a predetermined value.

3. A method as defined in claim 1, further comprising the steps of measuring the moisture content of conditioned tobacco, and adjusting the exchange of heat between the tobacco stream and said other fluid in stepwise fashion when the measured moisture content of conditioned tobacco deviates from a predetermined value.

4. A method as defined in claim 3, wherein said one fluid exchanges heat with the tobacco stream before the tobacco exchanges heat with the other fluid.

5. A method as defined in claim 3, further comprising the step of changing the ratio of surplus moisture which is expelled by said fluids.

6. A method as defined in claim 1, wherein at least one of said fluids is heated air.

7. A method as defined in claim 1, wherein at least one of said fluids is steam.

1 1 12 8. A method as defined in claim 1, wherein one of said References Cited 115115221: brought into direct heat exchange contact with UNITED STATES PATENTS 9. A method as defined in claim 1, wherein the amounts 2768629 10/1956 Maul lam-140 of moisture expelled from the tobacco by one of said 5 SAMUEL KOREN, Primary ami r.

22:: 5;??? ammmts 1018mm expelled by the J. H. CZERWONKY, Assistant Examiner.

10. A method as defined in claim 1, wherein the tobac- US. Cl. X.R.

c0 stream contains particles of shredded tobacco. 34-31 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,429,317 February 25, 1969 Hans Koch et al.

In the heading to the printed speclfication, lines 3 to 5, "Hans Koch, Meindorferweg 22, Hamburg-Rahlstedt, Germany, and Waldemar Wochnowski, Eulenkrugstrasse 143, Hamburg-Volksdorf, Germany" should read Hans Koch, Hamburg-Rahlstedt, Germany, and Waldemar Wochnowski, Hamburg volksdorf, Germany, assignors to Hauni-Werke Korber & Co. K. G., Hamburg-Bergedorf, Germany Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

